For a new shooter, I wouldn't personally recommend a .45, and especially one that is polymer-framed. There's no shame in starting with a 9mm, and I think it's very wise. The odds are that you will advance quicker with a smaller caliber. The 9mm is a fine caliber, and good for self-defense when loaded with hollow-points. Just my .02

The Glock 21 is a brick of a gun. Huge grip, giant thick slide. If you're a big guy, you might make it work. Difficult to carry concealed, even for a big man. Gun kicks a little, too, compared to a 9mm.

I see little need to carry a huge .45 when modern loads in smaller calibers (9mm, .40, etc.) work so well, and fit in smaller guns. I put my .45 away several years ago and rely primarily on 9mm Glocks.

I am a big guy (6'5") with big hands. Perhaps thats why the instructor recommended the .45 to me. Sounds like I'll just have to handle both and see what I think will work.

Being able to "handle" a caliber has much more to do with training and experience with a handgun than it does with physical size. Having said that, you are on the right track. Handle them, and more importantly, shoot them if you can before making a purchase. Good luck.

The Glock 21 will perform the task quite well but so will a number of others. It is always reccomended that a new shooter try several different models and calibers before buying. You need a feel for what is available and the difference between them in order to make an informed choice.

Glock, Smith & Wesson, Springfield and some others have competative equivalents in all standard calibers.

Rent some at a range and have a bit of fun prior to spending the big bucks.

I can palm a basketball, but I still prefer the SHAPE of an XD or M&P grip.

I shot the M&P this week with the large backstrap in it.... LOVELY... But like I said above, I'm 6'4" with hands to match (see my Avatar)...

Shoot a bunch of them... Glocks, XDs, M&Ps, Sigs, anything you can get your hand on.... Your taste will change with time. Mine has... I agree with a 9mm, simply because it is 1) perfectly adaquate for defense, and 2) HALF as expensive to feed as the 45.

More rounds down range, equals more confidence with the gun, and much smaller groups at speed.